Use of a high purity imidazoline based amphoacetates as surface active agents

ABSTRACT

Increased foam quality and resistance to hydrocarbon defoaming for foams used in well boring and stimulation processes as well as secondary and tertiary oil recovery is obtained using imidazoline-based amphoacetates of higher purity, containing essentially negligible amounts of unalkylated amido amines, lower amounts of glycolic acid salts and monochloroacetate salts. 
     The higher purity amphoacetates can be obtained via processes utilizing precise pH control during the reaction of imidazoline, or its open-chain derivatives, with alkylating agents, e.g. sodium monochloroacetate. These higher-purity amphoacetates contain essentially fully alkylated products and lower amounts of glycolic acid derivatives, even though a ratio of monohaloalkylate to substituted imidazoline, or its open-ring derivative, of less than 1.5:1.0 and close to 1.0:1.0 is used.

RELATED APPLICATIONS

The present application is a divisional of application U.S. Ser. No.08/446,393 that was filed on May 22, 1995 U.S. Pat. No. 5,614,473.

This invention relates to a surfactant composition having excellentfoamability and stability in a fresh water or high electrolyteatmosphere which may contain crude oil and/or hydrocarbon mixtures thatis adapted for use in geothermal or air drilling or stimulationoperations and secondary and tertiary oil recovery from undergroundoil-containing formations which use foam, such as CO₂ drive processes.

BACKGROUND OF INVENTION Field of the Invention

This invention relates to a method of increasing the recovery of oilfrom underground subterranean formations.

In drilling a bore into the earth, universally it has been the practiceto circulate a liquid, such as water, oil, a water-in-oil emulsion, oran oil-in-water emulsion, usually with mud solids suspended therein, toand from the drilling zone during the drilling operation. Circulatingdrilling fluids, generally known as a drilling mud, removes drilledsolids from the bit and lifts cuttings from the bore to keep the drillclean and lubricated. The drilling liquid is circulated under highpressure to assure entrapment of cuttings and expulsion of mud from thebore hole.

In newly discovered oil fields, oil will usually be recovered from aproducing well under the natural pressure of the fluids present in theporous reservoir rocks (primary recovery). The naturally occurringpressure in the formation decreases as the fluids are removed and about5% to 20% of the oil present in the formation is recovered.

Secondary recovery methods are used to recover more of the oil, such asby injecting a fluid into the reservoir to drive additional oil out ofthe rocks, e.g., waterflooding. Waterflooding has its own limitations asit is immiscible with oil and as the water displaces the oil, oilremaining in the reservoir reaches a limiting value known as "theresidual oil saturation" and oil no longer flows. There is a strongcapillary action which tends to hold the oil in the interstices of therocks. The amount of oil recovered by secondary techniques is usuallyfrom about 5% to 30% of the oil initially present.

In recent years, more attention has been directed to enhanced recoveryor tertiary recovery techniques. These tertiary recovery methods areused to recover the residual oil by overcoming the capillary forceswhich trap oil during waterflooding, such as by adding surfactants tothe flood to decrease the interfacial tension and thus allow oildroplets to move to producing wells.

Secondary recovery of oil is also possible by the miscible fluiddisplacement process. Propane, for example, would be an appropriatematerial to utilize for it is fully miscible with oil.

The use of crude oil miscible solvents such as propane alone or incombination with kerosene to displace crude oil through a formation iswell known, as, for example, in the teachings of Morse in U.S. Pat. No.3,354,953.

Some wells have been successfully drilled at a reduced pressure using acompressed gas, such as air which is pumped into the well at thedrilling site. This compressed gas flows rapidly up the well bore aroundthe drill collar carrying with it the drilled solids, thus removing themfrom the drill hole. While the drilling operation is essentially a dryprocess, in many formations water enters the bore hole from adjacentwater-containing strata or trapped underground water.

There are many advantages of the gas drilling method over the moreconventional mud drilling method. However, one difficulty in mist or drygas drilling where water seeps into the bore and accumulates in thedrilling zone, is that the drilled solids tend to agglomerate as thedrill rotates. These agglomerated masses become too heavy to be liftedout by the gas so that antiballing agents, and foaming agents must beintroduced into the bore to prevent this condition.

The technology of air and mud drilling has been combined in an attemptto provide drilling foams which have greater lifting strength than airbut which do not have the pressure limitations of drilling muds.

The rheological properties of aqueous foams are of great importance fora number of applications in petroleum production. These propertiesinclude high flow rates in tubes or pipes and in porous media such asoil-bearing sandstones. Aqueous foam has advantages in oil fields thatcontain viscous oil in low pressure reservoirs. In these operations, thefoam raises to the surface not only sand pulverized by the bit but alsopebbles and rocks of considerable size.

It is also known in the art that oil not directly recoverable by directpumping can be displaced and recovered from a subterranean reservoir byusing stimulation or secondary and tertiary recovery methods such as byinjecting a drive fluid containing pressurized gas, and particularly CO₂in substantially liquid form, water and a surfactant or by fracturingthe rock strata. Examples of this type of process can be found in U.S.Pat. Nos. 4,502,538 and 4,799,547.

It is noted that in the CO₂ drive system, use is made of a surfactant toform a "foam" which reduces the mobility of the CO₂ in the reservoir. Itis well recognized in the art that many reservoir flood or driveprocesses, including those utilizing CO₂ suffer from a tendency ofinjected fluids to sweep oil from only a limited area of the reservoir.The fluids break through to the recovery well before they have theopportunity to efficiently invade and displace oil from the reservoirrock.

The requirements for utilization of an aqueous foam in subterraneanformations include high stability with waters containing quantities ofsoluble salts, such as sodium chloride, calcium salts and/or magnesiumsalts and capability for handling a variety of foam breaking elements,e.g., hydrocarbon tolerance from such as crude oil and solids. Further,the foam must not degrade under extremes of the physical environment ofuse such as drilling pressure temperature, earth particles and the like.

In addition, the most important performance characteristics of asurfactant used in a CO₂ drive process is its ability to maintainexcellent foam generation and stability properties and thus maintaincontrol over mobility of the CO₂ in the presence of a wide variety ofcrude oils. The surfactant used in the CO₂ drive process should besubstantially less sensitive to compositional variations and changes inthe crude oil deposit as this can seriously affect the foam holdingcharacteristics of the surfactant.

Historically, alcohol ether sulfates have been used for CO₂ mobilitycontrol agents. Alcohol ether sulfates provide an overall cost advantagebecause of a production increase.

It is an object of this invention to proved a surfactant compositionhaving excellent foaming power and high tolerance for aqueous solutionscontaining electrolytes and/or hydrocarbons for use in oil well bores,such as for drilling, stimulation and secondary and tertiary oilrecovery.

It is now been found that improved foam control can be obtainedutilizing a specified group of amphoteric surfactants.

SUMMARY OF THE INVENTION

It has been now found that the foam holding characteristics of foam fromsurfactants utilized in oil wells, such as in well drilling, airdrilling, foam fracturing, stimulation or gas (CO₂) drive processes forsecondary and tertiary oil recovery can be improved by using a new andimproved high purity imidazoline based amphoacetate surfactant alone orin combination with other surfactants as will be more fully outlinedhereinafter. The surfactant combinations of the invention show reducedfoam detriment due to contact with hydrocarbons and more tolerance toconventional anionic foaming agents presently in use in the oilindustry. These features will become more fully evident in thedisclosure which follows.

DETAILED DESCRIPTION OF THE INVENTION

The improved amphoacetate surfactants used in the present invention canbe depicted by the formula:

    RC(O)--NH--CH.sub.2 CH.sub.2 --N--[(CH.sub.2).sub.n X] CH.sub.2 COOM FORMULA I

wherein R is an aliphatic radical containing from about 5 to about 19carbon atoms per molecule, X is OH or NH₂ and _(n) is an integer of from2 to 4 inclusive, and wherein M is a metal. Preferably, R is analiphatic radical containing a majority of from about 8 to about 18carbon atoms per molecule, X is OH and _(n) equals 2.

These improved amphoacetate surfactants can be prepared by new processeswhich involve the use of controlled pHs during the entire reaction andparticularly during the alkylation portion of the process, such as bycontrolled addition of an appropriate base slowly or automatically inresponse to a pH metering device to maintain a constant pH; or a seriesof staged additions of base, which are calculated to maintain the pHwithin the desired range and the like. Products of higher purity may beobtained by exposing the imidazoline to conditions which favor ringopening prior to alkylation followed by reaction with the alkylatingagent, e.g., sodium monochloroacetate, under carefully controlledconditions. By conducting the reaction of imidazoline or its ring openedderivative with the haloacetic acid salt under carefully controlled pHand temperature conditions during the reaction allows the reaction toproceed with lower molar ratios of substituted imidazoline or itsderivatives to monohaloacetate salt resulting in a higher puritysubstantially fully alkylated product (less by-product unalkylatedamide, glycolic acid, NaCl and residue haloacetate salt). Glycolic acidis formed from the haloacetate salt and is usually compensated for byexcess monohaloacetate.

The imidazoline starting materials useful in the practice of theinvention can be represented by the formula: ##STR1## wherein R, n and Xare as defined hereinbefore.

When R is derived from a natural source, R can be mixture of saturatedand unsaturated aliphatic radicals derived from coconut oil or similarnatural oil sources such as palm kernel oil or animal fat sources suchas tallow. In that case, each R being a mixture of alkyl radicalscontaining from about 5 to 18 carbon atoms. R can also, preferably bederived from a saturated portion of coconut oil or similar naturalvegetable oil. In the case of coconut oil fatty acid, each R ranges fromabout 6 to about 18 carbon atoms. These ranges are given as coveringabout 90% of the R groups in the compound. Since these R groups arederived from natural sources, they can contain small amounts of othercarbon chains. In addition, imidazolines based on single carboxylicacids, e.g., lauric acid, or other cuts, as suited for the particularapplication, may be used.

The imidazolines used in the present invention should be insubstantially pure form. "Substantially pure" is intended to meansubstantially free from fatty acids, aminoethylethanol amine, amidoesters and diamides. For the purposes of the invention, the presence ofamido amines is acceptable. Any convenient method for preparing theimidazoline can be used.

Examples of the starting imidazolines include 2-heptylimidazoline,2-dodecylimidazoline, 2-heptadecylimidazoline,1-hydroxyethyl-2-dodecylimidazoline,1-hydroxy-ethyl-2-heptadecylimidazoline, and the like. Examples ofsingle fatty acids and fatty acids mixtures that can be used to preparethe imidazolines can include coconut oil fatty acid, palm kernel oilfatty acid, capric, caproic, caprylic, hexadecadienoic, lauric,linoleic, linolenic, margaric, myristic, myristoleic, oleic, palmitic,palmitoleic, stearic and the like.

The imidazoline is reacted under conditions which will favor opening ofthe imidazoline ring prior to the alkylation reaction. In one embodimentof the invention, the imidazoline can be heated under an elevated pHranging from about 8.5 to about 10 to facilitate opening of at least amajority of the imidazoline rings. In an alternative embodiment, theimidazoline can be admixed with the monohaloacetate at elevated pH underconditions that favor ring opening. In a third embodiment, themonohaloacetate can be added to the imidazoline along with the additionof base under conditions y that maintain the pH within the range ofabout 9 to about 10 during the addition.

For alkylation the imidazoline or ring opened derivative is heated witha salt of a monohaloacetate preferably in aqueous solution prior toadmixture with the imidazoline. The salt can be prepared from the acidjust prior to the reaction with an excess of base to provideneutralization for the hydrohalic acid formed during the reaction of theimidazoline with the haloacetate salt. The excess pH preferably rangesfrom about 8 to about 10. The haloacetate salt can be purchased orprepared elsewhere, dissolved in water and used as such or preferablywith an added amount of base corresponding to the excess discussedabove.

Examples of suitable monohaloacetate salts wherein the cationic portionis an alkali metal ion include sodium monochloroacetate, sodiummonobromoacetate, and potassium monochloroacetate and potassiummonobromoacetate. The preferred monohaloacetates are the sodium andpotassium salts of monochloroacetic acid.

Examples of suitable alkalis that can be used in the process of theinvention include sodium hydroxide, potassium hydroxide, sodiumcarbonate, potassium carbonate, sodium bicarbonate, potassiumbicarbonate and the like. Preferably, the alkali is sodium and/orpotassium hydroxide.

The mole ratio of the monohaloacetic acid or its salt form to theimidazoline or amine is preferably greater than one. At amounts of lessthan one, insufficient monchaloacetic acid salt is present to effectcomplete alkylation leaving the product contaminated with the amidoamine which has no surface activity. A surprising result of the presentinvention is that the ratio can be kept as low as possible with only aslight excess needed to drive the reaction substantially to completion.It is possible by means of the invention to keep the ratio as low as1.05:1. Preferably the ratio ranges from about 1.05:1 to about 1.5:1,more preferably 1.05:1 to about 1.4:1 and most preferably 1.05:1 toabout 1.2:1.

The reaction is generally conducted at a temperature conducive to thereaction as is well known in the industry. Reaction temperatures for themain reaction can range as high as 95° C., preferably and morepreferably between about 75° C. and about 85° C. between about 50° C.and about 95° C. The reaction can be heated after the main reaction isconsidered complete to insure completeness of reaction. Temperaturesduring this portion of the reaction can range as high as 100° C. Thereaction times are sufficient to accomplish each desired reaction stepand can be easily determined by a skilled artisan.

In general, the monohaloacetic acid or salt is blended with theimidazoline at a rate as fast as possible and practical to admix thereactants completely. Because pH control is essential the reactants,especially the base, are added at such a rate as to prevent pH risesabove about pH 10. Care is taken to avoid localized "hot spots" duringthe addition of base. The base is added incrementally to avoid any pHsurge.

The careful pH and temperature control during the reaction allows thereaction to proceed with less sodium monohaloacetate salt resulting in ahigher purity product (less by-product unalkylated amide, glycolic acid,NaCl and residue haloacetate salt). The compositions of the presentinvention are characterized by levels of unalkylated amide of less thanabout 3.5%, preferably less than about 2.0% and more preferably lessthan about 0.5% unalkylated amide; glycolic acid of less than about4.5%, preferably less than about 3.5 and more preferably less than about2.5% glycolic acid alkali metal salt, e.g., sodium chloride, of lessthan about 27%, preferably less than about 23% and more preferably lessthan about 20% salt all on an actives basis.

The details of the process can be more fully seen in U.S. Ser. No.08/135,094, the disclosure of which is hereby incorporated by reference.

Because of the improved purity, the products of the invention exhibitsuperior surfactant properties, greater formulating flexibility, inaddition to being economically more attractive as compared to productsobtained by purification of materials prepared by process of the priorart.

The amphoacetate surfactants as described above, exhibit enhancedwetting speed, greater surface tension reduction, high foaming and foamstabilization properties particularly in the presence of hydrocarbonswhich are known foam breakers, low toxicity, and excellent compatibilitywith other anionic, ionic and nonionic surfactants. These products arestable over a wide pH range and are biodegradable.

In addition to oil wells, the present invention can be used in anysystem that relies on maintaining a foam while in contact withhydrocarbons for effectiveness. Examples of such foams include firefighting foams which can, in fighting fires such as airliner or chemicalplant fires, come into contact with hydrocarbons.

The compositions of the invention can be used under the same mixing,temperature, pressure, and additional additives as are presently used inthe art in preparing secondary, and tertiary foaming systems as well asfoam formulating for drilling or stimulation, such as those generallybased on anionic surfactants. These can be easily determined by one ofordinary skill in the art. In addition to the surfactant which is thesubject of the invention, there can also be included foam stabilizers,foam boosters, pour point depressants and other common ingredients. Ithas been particularly found that more effective results can be obtainedusing a hydrocolloid, and preferably xanthan gum, (from about 0.01% toabout 1.0% by weight based on the weight of the surfactant containingsystem of water, salts and foaming or surfactant package) as an adjuvantto the surfactant disclosed herein. The surfactant disclosed herein isgenerally used in an amount effective to prepare a foam alone or toprepare and stabilize the foam when used with other foamablesurfactants. Illustrative amounts of the surfactant disclosed hereinrange from about 0.01% to about 1.0% by active weight based on theweight of the surfactant containing system of water, salts and foamingor surfactant package.

The present invention will now be more fully illustrated in the exampleswhich follow. The percentage purity of the products prepared in theexamples and as given in the claims are on an actives basis by weightbased on the amount of active material present in the product asdetermined by subtracting the amount of sodium chloride, glycolic acidand amido amine from the as is solids of the reaction.

The surfactant of the invention as used in the examples is acocoamphoacetate of Formula I wherein R is coco, n is 2, m is sodium andthe surfactant composition is 37% active. This 37% active surfactantwill be identified in the examples as "COCOAMPHO ACETATE". As usedherein, GEROPON® AS-200 is a sodium cocyl isethionate anionicsurfactant, MIRATAINE® CB is a cocamidopropyl betaine, MIRATAINE® CBS isa cocamidopropyl hydroxy sultaine, MIRANOL® C2M-NP is a disodiumcocoampho diacetate amphoteric surfactant; MIRANOL® C2M-SF is a disodiumcocoampho dipropionate amphoteric surfactant, RHODACAL® A246/L is asodium alphaolefin sulfonate anionic surfactant; RHODACAL® DS-10 is asodium dodecylbenzene sulfonate anionic surfactant; RHODAPEX® CD128 isan ammonium alcohol ether sulfate anionic surfactant, and RHODOPOL® XGDis an aqueous dispersible xanthan gum.

EXAMPLE I

Various surfactant blends were tested to determine the ability of asurfactant(s) to maintain a foam when in direct contact with ahydrocarbon.

CRUDE ON BOTTOM PROCEDURE

A brine containing 11.73 grams/liter calcium chloride, 6.21 grams/litermagnesium chloride and 37.84 grams/liter sodium chloride was prepared(Brine A).

The pH of a 200 cubic centimeter sample of Brine A was adjusted to pH5.0-5.5 by bubbling CO₂ through the sample. To this 200 cubic centimeteraliquot was added 1.0 cubic centimeter of a test material (0.5%).

Brine A, containing the test surfactant was mixed for thirty seconds athigh speed in a blender (Waring). Foam heights were recorded initiallyand after thirty and sixty seconds. The sample was then remixed in theblender for an additional thirty seconds and 200 cubic centimeters ofthe foam was transferred to a graduate cylinder containing 5 cubiccentimeters (2.5%) crude oil. The weight of the 200 cubic centimeters offoam was measured to calculate foam quality. The ratio of foam to liquidor the % foam was measured initially and after 5, 10, 30, 60, 120minutes and 16 hours.

                                      TABLE I                                     __________________________________________________________________________    FOAM EVALUATION                                                               BRINE FORMULATION "A"  WITH 1% MOBIL CRUDE ON BOTTOM                          .05% OF A (75% CD128:25% X)                                                   WITH 0.2% RHODOPOL XGD                                                                   RHODAPEX                                                                             RHODACAL                                                                             MIRANOL                                                                             GERAPON                                                                             MIRATAINE                                                                            MIRATAINE                                                                            COCOAMPHO                             CD 128      DS1O                                                                               C2M-SF                                                                                AS200                                                                               CB                                                                                     CBS                        __________________________________________________________________________                                                       ACETATE                    FOAM HEIGHT (CM)                                                                   WARING BLENDER                                                           INITIAL                  9 9.5                                                                                     9                                                                                                    2.3               AFTER 30'                99.5                                                                                      9                                                                                                    2.2               AFTER 60'                8.95                                                                                8.1                                                                                 9                                                                                                    2.1               FOAM PERSISTENCE                                                              W/ RESPECT TO TIME                                                            INITIAL                        98                                                                                        98                                                                                     95                          5'                           98                                                                                        98                                                                                             60                     10'                       98                                                                                        98                                                                                             55                 30'                           93                                                                                        92                                                                                             50                      80'                      51                                                                                        72                                                                                             45                120'                           34                                                                                        23                                                                                             45                16 H              0      0    0                                                                              0     0      0      38                         FOAM QUALITY                                                                                                 78                                                                                        75                                 __________________________________________________________________________                                                       42                     

                                      TABLE II                                    __________________________________________________________________________    FOAM EVALUATION                                                               BRINE FORMULATION "A"  WITH 1% MOBIL CRUDE ON BOTTOM                          WITH .05% SURFACTANT X                                                        WITH 0.2% RHODOPOL XGD                                                        __________________________________________________________________________    X =                 50% RHODAPEX                                                                            75% RHODAPEX                                                                            50% RHODAPEX                                              CD126             CD128                                                                                   CD128                                             50% COCOAMPHO                                                                           25% COCOAMPHO                                                                            50% MIRANOL                                              ACETATE   ACETATE   C2M-NP                                __________________________________________________________________________    WARING BLENDER FOAM HEIGHT (CM)                                               INITIAL                                            7                          AFTER 30"                                          7                          AFTER 60"                                          7                          FOAM PERSISTENCE WITH                                                         RESPECT TO TIME (% FOAM)                                                      INITIAL                                            98                         AFTER 5'                                           96                         AFTER 10'                                          92                         AFTER 30'                                          79                         AFTER 60'                                          75                         AFTER 120'                                         71                         AFTER 16 h                                      TRACE                         FOAM OUALITY                                                                  WEIGHT OF 200 cc OF FOAM (GM)                                                                           58                       52                         FOAM QUALITY                                       74                         __________________________________________________________________________     **VERY LOW DENSITY FOAM                                                  

                  TABLE III                                                       ______________________________________                                        FOAM EVALUATION                                                               BRINE FORMULATION "A"  WITH 1% MOBIL CRUDE ON BOTTOM                          0.5% OF SURFACTANT X                                                          ______________________________________                                        X =          50% RHODACAL  50% RHODAPEX                                                                        CD128                                                             50% COCOAMPHO                                                                       50% COCOAMPHO                                                   ACETATE       ACETATE                                            ______________________________________                                        WARING BLENDER                                                                FOAM HEIGHT (CM)                                                              INITIAL                               8.7                                     AFTER 30"                             8                                       AFTER 60"                             8                                       FOAM PERSISTENCE                                                              WITH RESPECT TO                                                               TIME (% FOAM)                                                                 INITIAL                                95                                     AFTER 5'                               80                                     AFTER 10'                              76                                     AFTER 30'                              72                                     AFTER 60'                              71                                     AFTER 120'                             67                                     AFTER 16 h                          TRACE                                     FOAM OUALITY                                                                  WEIGHT OF 200 cc                                                                           84            50                                                 OF FOAM (GM)                                                                  FOAM QUALITY                          75                                      ______________________________________                                    

                  TABLE IV                                                        ______________________________________                                        FOAM EVALUATION                                                               BRINE FORMULATION "A"  WITH 1% MOBIL CRUDE ON BOTTOM                          0.5% OF SURFACTANT X                                                          ______________________________________                                        X =          33% RHODAPEX  33% RHODAPEX                                                                            CD128         CD128                                                   33% RHODACAL   33% RHODACAL                                                           A246/L    246/L                                                        33% COCOAMPHO MIRANOL                                                      ACETATE         C2M-NP                             ______________________________________                                        WARING BLENDER                                                                FOAM HEIGHT (CM)                                                              INITIAL                                 4.6                                   AFTER 30"                               4.6                                   AFTER 60"                               4.6                                   FOAM PERSISTENCE                                                              WITH RESPECT TO                                                               TIME (% FOAM)                                                                 INITIAL                                98                                     AFTER 5'                               96                                     AFTER 10'                              90                                     AFTER 30'                              85                                     APTER 60'                              75                                     AFTER 120'                             72                                     AFTER 16 h                           60                                            FOAM OUALITY                                                             FOAM OUALITY                                                                  WEIGHT OF 200 cc                                                                           60            75                                                 OF FOAM (GM)                                                                  FOAM QUALITY                           62.5                                   ______________________________________                                         **VERY LOW DENSITY FOAM                                                  

                                      TABLE V                                     __________________________________________________________________________    FOAM EVALUATION                                                               BRINE FORMULATION "A"  WITH 1% MOBIL CRUDE ON BOTTOM                          WITH 0.5% OF SURFACTANT X                                                     WITH 0.2% RHODOPOL XGD                                                        __________________________________________________________________________    X =                 15% ETHYLENE                                                                            15% PROPYLENE                                                                           15% ETHYLENE                                                                 GLYCOL          GLYCOL                                                                GLYCOL                                             29% RHODAPEX                                                                              29% RHODAPEX                                                                           29% ⋄                                            CD128               CD12B                                                     29% RHODACAL                                                                              29% RHODACAL                                                                           29% RHODACAL                                             246/L               A246/L                                                                               A246/L                                             29% COCOAMPHO                                                                            29% COCOAMPHO                                                                           29% COCOAMPHO                                            ACETATE   ACETATE   ACETATE                               __________________________________________________________________________    WARING BLENDER FOAM HEIGHT (CM)                                               INITIAL                                            7                          AFTER 30"                                          7                          AFTER 60"                                          7                          FOAM PERSISTENCE WITH                                                         RESPECT TO TIME (% FOAM)                                                      INITIAL                                             98                        AFTER 5'                                            98                        AFTER 10'                                           95                        AFTER 30'                                           90                        AFTER 60'                                           83                        AFTER 120'                                          77                        AFTER 16 h                                          67                               FOAM QUALITY                                                           WEIGHT OF 200 cc OF FOAM (GM)                                                                           65                        53                        FOAM QUALITY                                     73.5                         __________________________________________________________________________     ⋄ Ammonium Ether Sulfate                                              **VERY LOW DENSITY FOAM                                                  

The results of these tests show that the cocoamphoacetate alone or incombination with a foaming agent provides good initial foam andstabilizes foam at times greater than 16 hours while in contact withhydrocarbon whereas other formulations not formulated in accordance withthe invention showed little to no foam after 16 hours.

EXAMPLE II

Based on the criteria for a CO₂ mobility control agent, a hydrocarbontolerant foam agent was developed which has the following formulation:

28.6% RHODAPEX® CD128

28.6% RHODOCAL® A246/L

28.6% COCOAMPHOACETATE (37%)

14.3% ETHYLENE GLYCOL

This formulation can be used as a CO₂ mobility control agents or as afoam agent for foam fracturing or air drilling. This composition issignificantly more tolerant than conventional anionic foam agentspresently in use in the oil industry.

While the invention has been explained in relation to its preferredembodiments, it is to be understood that various modifications thereofwill become apparent to those skilled in the art upon reading thespecification. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications as fall withinthe scope of the appended claims.

What is claimed is:
 1. A process for treating a surface with sustainablefoam by means of a foamable surfactant wherein the foamable surfactantcomprises a substantially pure substituted imidazoline-derivedamphoacetate containing as a component thereof a compound of theformula: ##STR2## wherein R represents an aliphatic radical containingfrom about 5 to about 19 carbon atoms per molecule, X is OH or NH₂, n isan integer of from 2 to 4 inclusive and M is a metal, said compositioncontaining less than about 3.5% unalkylated amide and less than about4.5% glycolic acid, wherein the amphoacetate is produced by a process inwhich the imidazoline ring is opened prior to alkylation.
 2. A processas recited in claim 1 wherein the composition contains less than about2.0% unalkylated amide.
 3. A process as recited in claim 1 wherein thecomposition contains less than about 3.5% glycolic acid.
 4. Acomposition as recited in claim 1 wherein the composition additionallycontains less than about 27% alkali metal halide salt.
 5. A process asrecited in claim 1 wherein X is OH.
 6. A process as recited in claim 1wherein R is derived from a member selected from the group consisting ofcoconut oil fatty acids, palm kernel oil fatty acids, capric, caproic,caprylic, hexadecadienoic, lauric, linoleic, linolenic, margaric,myristic, myristoleic, oleic, palmitic, palmitoleic, and stearic acidsand mixtures thereof.
 7. A process as recited in claim 1 wherein M is analkali metal.
 8. A process as recited in claim 1 wherein R is derivedfrom coconut oil fatty acids, n is 2, X is OH and M is sodium.